Personally I find it difficult to critique UML when I am not sure exactly what you are trying to achieve, but I'll give it a go. It looks good except for a couple of things that I noticed.
First of all, you have a User having a Family, I think it could possibly be better to have the family having a list of users and functions such as isFamilyMember($user) . I think this would be a cleaner solution.
The other thing I noticed is that Users, Families and Companies all have a Bank object, and Users also have a Family and a list of Companies. This to me seems a bit too much, perhaps you need to think about what you are trying to achieve with your Bank object.
Other than that, the UML looks like a good start for how these classes might interact, but you need to keep in mind that PHP is not an object-oriented language although it does feature some support for classes.
Thank you very much for giving it a try, I understand it is difficult. Your comments made me start overthink my UML.
Your idea about isFamilyMember is quite a good idea and I will go for it.
You are also right about my bank, Users, Families and Companies will now implent the Bank class.
The goal I am trying to achieve here is setting up a decent framework for a browser game. I hope that makes it clearer for you and other people that are willing to comment on my UML. I will update the picture within the next hour.